Magnetoresistive (MR) devices can be used in many applications, including, for example, hard disk drive read sensors and magnetic random access memory (MRAM) devices. The electrical resistivity of a MR device changes when that device is subjected to an external magnetic field. When the MR device is subjected to an external magnetic field of a first polarity, the resistance is a higher value, and when the device is subjected to an external magnetic field of a substantially opposite polarity, the resistance is a lower value. If the high-resistance state represents a 0, and the low-resistance state represents a 1, or vice versa, MR devices can be used to store information, for example, on a MRAM device. Similarly, MR devices can be used in read sensors to retrieve information from magnetic media, such as, for example, from a magnetic hard disk drive storing bits.
The magnetoresistance (MR) ratio of a MR device is the ratio of the difference in resistance between the high- and low-resistance states to the resistance of the low-resistance state. In both MRAM and hard disk drive applications, it is desirable for MR devices to exhibit a high MR ratio to reduce the likelihood that a 0 is stored as or mistaken for a 1 and vice versa.
Thus, there is an ongoing need to improve the MR ratio of MR devices.